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Electronic Line Pack with Opto Electronic Line Isolation

IP.com Disclosure Number: IPCOM000088532D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Patten, MA: AUTHOR

Abstract

This low-cost telephone pack is small in size, but provides the necessary isolation and two-to-four wire conversion at audio frequencies without the use of a transformer. The circuit is designed for use in a pulse amplitude modulation, time-division multiplexing telephone switching system.

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Electronic Line Pack with Opto Electronic Line Isolation

This low-cost telephone pack is small in size, but provides the necessary isolation and two-to-four wire conversion at audio frequencies without the use of a transformer. The circuit is designed for use in a pulse amplitude modulation, time-division multiplexing telephone switching system.

Audio frequency signal voltage from the switching components enters the line pack at terminals 10 and 12. The signal is amplified by amplifying circuits 14 and 16 comprising two opto-electronic isolating coupling devices 17, 18 which provide gain, and from which a differential signal is delivered through load resistors 22, 24, to line terminals 26, 28. The line terminals have conventional 48-volt direct potential across them. Load resistors 22, 24 carry operating current to the telephone and limit that current in the event of a short circuit on the line.

The output of the devices 17, 18 is applied to another pair 33, 34 of opto- electronic devices coupled by a capacitor 36 to a balancing amplifier 35, to which an equal and opposite signal is adjusted by varying the values of a potentiometer
38. Thus, only an attenuated signal from the sources described reaches the terminals 42, 44. The total phase shift due to capacitive coupling is equalized for optimum hybrid balancing.

The audio frequency signal from the line terminals 26, 28 is amplified by the amplifier circuit 34 and is delivered at the terminals 42, 44 with no cancelling input from the balancing network. No direct potential offset from the line pack input is present at the output because of the isolating characteristics of the opto-electronic devices...